Because of demands for improvements in fuel efficiency and acceleration performance, the numbers of speed change ratios or speed ranges available for transmissions have increased (refer to, for example, Japanese Laid-Open Patent Publication No. 2000-266138).
However, the increased number of speed change ratios or speed ranges also involves an increase in the number of engaging elements, which leads to an increase in the weight and cost of the transmission. For example, in the transmission described in patent reference 1, seven engaging elements are used for realizing six or seven speed change ratios as speed ranges in forward drive.